1. Field of the Invention
The present invention relates to air brakes for motor vehicles and trailers, and more particularly relates to the air supply system for such brakes.
2. Description of the Problem
Mechanical braking systems for heavy trucks have been largely displaced by more reliable air and hydraulic brakes. Air brakes, requiring no hydraulic liquid, are clean and have fewer environmental concerns should a coupling fail than hydraulic units and have proven popular. An air brake system usually includes a compressor, two air storage tanks, various control valves and air lines. Pressure regulating systems control the compressor. Conduits and valves control application of air pressure to pneumatically driven components. The compressor draws air from the atmosphere and delivers it to one of the tanks which functions as a first stage tank often called the wet tank. From the wet tank the air passes to a second stage tank often called the dry tank from which the air is distributed.
Air brakes can be vulnerable to moisture and because the source of air for the compressed air system is the ambient atmosphere, which may hold much moisture, an air drying system is usually provided between the compressor and the wet tank. Obviously, this air drying system should be highly reliable. At the same time, the air drying system should not complicate assembly or maintenance of a vehicle and it should not be excessively expensive.
Contemporary practice favors desiccant based air drying systems. A desiccant based air dryer provides a molecular sieve through which air passes. The molecular sieve comprises a hydrophillic compound which pulls the moisture from the air. Over time the molecular sieve can break down from repeated cycles of wetting and drying, or from contamination from other impurities. Periodic replacement of the desiccant may be required.
Desiccants have been provided in replaceable, spin-on canisters similar to those used for replaceable oil or fuel filters. The hydrophillic material is located in an outer chamber so that inlet air from the compressor enters the outer chamber, passes through the hydrophillic material, and then passes to the outlet via an inner core. While spin-on canisters are readily replaceable, the amount of water they can remove is dependent upon the length of the flowpath through the desiccant. The space in the canisters is limited and they often cannot be readily lengthened to improve air drying.
The addition of canisters to the air brake system has also added to the complexity of an already complicated pneumatic plumbing system. U.S. Pat. No. 6,074,462 to Quinn is directed to the problem. Numerous air lines have been required to connect the pressure tanks to the brake and other components. Air lines are provided interconnecting the tanks. The tanks have often been located, spaced from one another, wherever room was available on the vehicle frame. The desiccant canister and compressor have also required air lines. Simplification of the entire system, consistent with providing effective and easily maintained air drying would be advantageous.
According to the invention there is provided a vehicle having an air supply system for a vehicle brake system. The air supply system is based on a compressor for supplying compressed air. The compressed or pressurized air is routed to an air dryer which includes a desiccant bed through which the compressed air flows. The desiccant bed is housed in an outer canister having opposite facing mating sides and a flow through pipe through the bed connecting the opposite facing mating sides. A first stage air tank, located along a first of the opposite facing mating sides, receives air from the air dryer through a port. A second stage air tank is located along the remaining one of the mating sides and communicates with the first stage air tank through the flow through pipe. The air dryer is mounted on tracks allowing it to withdrawn from between the air tanks for replacement or service.
Additional effects, features and advantages will be apparent in the written description that follows.